Previous spin-fluctuation theories yielding the strong coupling corrections ..delta..beta-bar/sub i/ to the five coefficients of the fourth-order invariants in the free energy functional are extended. First, the superfluid part of the susceptibility is calculated up to order ..delta../sup 4/for all momenta and frequencies and the contribution arising from p-wave fluctuations of the order parameter is included. Then the frequency sums yielding the ..delta..beta-bar/sub i/ are calculated by taking into account the full momentum and frequency dependence of the superfluid susceptibility and the spin fluctuation propagator. The results for the ..delta..beta-bar/sub i/ are plotted vs. a cutoff q/sub c/ on themore » momentum integration for spin-fluctuation parameters IequivalentN(0)I=0.75 and I=0.95. The cutoff takes into account in a rough way the effect of additional terms in the free energy functional which were neglected in previous theories. These additional terms are due to the implicit dependence of the superfluid susceptibility on the spin-fluctuation parameter I via the gap parameter ..delta... The gap equation providing the relation between ..delta.. and I is derived in the weak coupling approximation. The cutoffs obtained by fitting the experimental values of the three combinations of ..delta..beta-bar/sub i/(arising from the measured specific heat discontinuities on the melting curve) are comparable to the cutoff obtained from the spin-fluctuation contribution to the weak coupling free energy (q/sub c/=0.3(2k/sub F/) for I=0.75). The corrections due to the momentum and frequency dependence of the superfluid susceptibility and the spinfluctuation propagator are large and point in the direction of better agreement with experiment: The ratio R/sub 1/ =..delta..beta-bar/sub 5//(..delta..beta-bar/sub 2/+..delta..beta-bar/sub 4/) decreases from 2 to about 1.2. It is concluded that spin-fluctuation theory in its present form cannot account quantitatively for the measured specific heat discontinuities on the melting curve.« less

Here, we report inelastic neutron scattering measurements over 7–1251 K in CaMnO 3 covering various phase transitions, and over 6–150 K in PrMnO 3 covering the magnetic transition. The excitations around 20 meV in CaMnO 3 and at 17 meV in PrMnO 3 at low temperatures are found to be associated with magnetic origin. We observe coherent magnetic neutron scattering in localized regions in reciprocal space and show it to arise from long-range correlated magnetic spin-waves below the magnetic transition temperature (TN) and short-range stochastic spin-spin fluctuations above T N. In spite of the similarity of the structure of themore » two compounds, the neutron inelastic spectrum of PrMnO 3 exhibits broad features at 150 K unlike well-defined peaks in the spectrum of CaMnO 3. This might result from the difference in the nature of interactions in the two compounds (magnetic and Jahn-Teller distortion). Ab initio phonon calculations have been used to interpret the observed phonon spectra. The ab initio calculations at high pressures show that the variations of Mn-O distances are isotropic for CaMnO 3 and highly anisotropic for PrMnO 3. The calculation in PrMnO 3 shows the suppression of Jahn-Teller distortion and simultaneous insulator-to-metal transition. It appears that this transition may not be associated with the occurrence of the tetragonal phase above 20 GPa as reported in the literature, since the tetragonal phase is found to be dynamically unstable, although it is found to be energetically favored over the orthorhombic phase above 20 GPa. CaMnO 3 does not show any phase transition up to 60 GPa.« less

We have studied the electronic structure and the distribution of magnetic moments in amorphous Fe metallic glass by means of first-principles calculations. Large periodic models containing 100 and 200 atoms in a cubic cell are constructed using the Monte Carlo technique. The electronic structures are calculated within the real-space OLCAO scheme using the spin-polarized potentials obtained from the crystalline calculation. Results are presented for the spin-projected density of states (DOS), the partial DOS, and spin magnetic moments. It is shown that spin moments in {ital a}-Fe is mainly determined by the minority spin band because the Fermi level is locatedmore » near the middle of this band. The site-specific distribution of Fe moments in an amorphous environment is analyzed as a function of local short-range order such as the number of nearest-neighbor atoms and the average nearest-neighbor distances. Extension of similar calculations to {ital a}-Fe{sub 1{minus}{ital x}}--B{sub {ital x}} metallic glasses is also discussed.« less